A so-called SOI (Silicon on Insulator) wafer, in which a single crystal silicon (Si) layer is provided on an insulating film such as an oxide film, is used as a substrate for device formation for the purpose of forming a MOS transistor excellent in radiation-resistant characteristics and latch-up characteristics and excellent at suppressing the short channel effect. Among SOI substrates, a less-defective SOI substrate to which a bonding technique has been applied is attracting attention. The use of such an SOI substrate as a substrate for optical device manufacture has come under review in recent years (e.g., Patent Documents 1 to 5).
Among methods for driving electro-optic devices, including a liquid crystal display panel (LCD), an active matrix method is a driving method which is commonly used for the reason that high definition is achieved due to high response speed if the method is applied to a display device and for other reasons.
The general configuration of such an active-matrix-driven electro-optic device is such that a liquid crystal layer is provided by sandwiching liquid crystal between two glass substrates of upper and lower glass substrates and that an upper electrode (counter electrode) common to the whole pattern is formed on the upper glass electrode while pixel electrodes and TFTs as switching elements for driving the respective pixel electrodes are provided on the lower glass substrate. An X electrode as a gate input unit of the TFT provided for each pixel and a Y electrode as a source input unit are patterned on the lower glass substrate. The input of an electrical signal to each TFT is controlled through these electrodes. With this control, each TFT as the switching element is controlled. Liquid crystal in an area between each pixel electrode and the counter electrode changes in orientation depending on the electric field generated between the upper and lower electrodes and functions as a liquid crystal shutter. That is, each pixel is driven by turning on/off the corresponding TFT as a switching element for a liquid crystal shutter.
Such a TFT has conventionally been provided in an amorphous Si (a-Si) or polycrystalline Si (poly-Si) film provided on a lower glass substrate. Since a TFT as a switching element is required to operate at high speed for high-speed control of pixel switching, the use of a single crystal Si TFT instead of an amorphous Si TFT or polycrystalline Si TFT has been considered, and the use of an SOI substrate having a single crystal silicon thin film on an insulating substrate has been considered. In other words, formation of TFTs in a single crystal Si layer provided on an insulator layer by means of bonding or the like allows much faster switching than the case of amorphous Si TFTs or polycrystalline Si TFTs.
Patent Document 1: Japanese Patent Laid-Open No. 11-145438
Patent Document 2: Japanese Patent Laid-Open No. 6-18926
Patent Document 3: Japanese Patent Laid-Open No. 11-163363
Patent Document 4: Japanese Patent Laid-Open No. 2003-282885
Patent Document 5: Japanese Patent Laid-Open No. 2002-110998
Patent Document 6: Japanese Patent No. 3048201